1. Field of the Invention
The present invention relates to a data communication system for data communication among plural stations, and more particularly to such a data communication system adapted for use in an image communication network composed of plural stations each comprising an image reading device and an image output device and mutually connected through transmission channels such as optical fibers for image communication among stations or within a station.
2. Description of the Prior Art
FIG. 1 shows an example of the image communication network utilizing a conventional image communication process, including image reading (reader) units 1a, 1c-1e; image output (printer) units 2a-2d; modulating/demodulating (modem) units 3a-3f; optical fiber communication cables 4a-4f connecting said modems 3a-3f; and cables 5a-5f connecting the readers 1a, 1c-1e with the printers 2a-2d or a memory 6f for temporarily storing the image signals.
In the image communication network of the above-described structure, the image signals read in the reader 1a can be transmitted to the printer 2a of the same station through the cable 5a for image recording, or transmitted through the modem 3a and the optical fiber 4a to other printers 2b-2d of other stations for image recording. Also in case of image editing such as image trimming, coordinate displacement or image synthesis the image signals have to be temporarily stored in the memory 6f for subsequent signal reading and image processing, and, in such case, the memory 6f can function as a terminal independent from the readers 1a, 1c-1e since said memory 6f is connected to the optical fibers 4a-4f through the modem 3f. Consequently the data transmission to the memory 6f can be designed with the substantially same principle as that for the data transmission to the printers 2a-2d.
However, for example, in case there is to be obtained a hundred copies from image signals stored in the memory 6f, the optical fibers 4a-4f are occupied during the transmission of the image signals one hundred times, so that other stations cannot achieve data communication through the optical fibers 4a-4f during the above-mentioned copying operation.
Also there have been proposed various communication control processes for avoiding data collision and achieving smooth data communication in the communication network. However such processes have not provided adequate procedures in case plural terminals or stations join the communication in the course thereof.